Acceptance of Murine Islet Allografts without Immunosuppression in the Inguinal Subcutaneous White Adipose Tissue Pretreated with bFGF

Abstract

Prevention of immune rejection without immunosuppression is a goal for transplant immunology. Previous report demonstrated that rejection of rat islet allografts in sc space of the back between low responder strains was prevented by pretreatment of the site with bFGF (AJT2014). However, it was not in the high responder combination of mice (BALB/c to C57BL/6). Here, we determined whether islet allografts in the inguinal subcutaneous white adipose tissue (ISWAT), a novel site of islet transplantation (tx), pretreated with bFGF are accepted without immunosuppression in mice. An agarose rod containing bFGF was buried in the ISWAT of a C57BL/6 mouse, and 1-3 weeks later 400 BALB/c islets (2 donors) were grafted in the space after the removal of a rod. Recipients were made diabetic by STZ (180mg/kg, iv) at 3 days prior to tx. Eventually, we found that 10μg bFGF/50μl/rod with 2 week interval is the optimal, in which 11/14 recipient mice remained normoglycemic (<200mg/dl) for more than 60 days. Removal of the ISWAT with islets promptly made recipient mice hyperglycemic again. Histologically, intact islets were seen in the ISWAT. In contrast, islet allografts (n=7) in the ISWAT pretreated with vehicle were rejected by 10 days. FACS revealed an expansion of CD8 T cells in the ISWAT rejecting but not accepting islet allografts. In the latter, IL-10+cells including Gr-1+ cells were seen. Re-tx of BALB/c islets (n=3) to the contralateral ISWAT of normoglycemic mice induced rejection of the initial BALB/c grafts and made recipient mice hyperglycemic again, while that of C3H (n=3) did not. These findings indicate that acceptance of murine islet allografts without immunosuppression was achieved when the ISWAT pretreated with bFGF was the site and that the acceptance appeared mediated by local rather than systemic unresponsiveness. Disclosure Y. Nakafusa: None. N. Nitta: None. M. Nakamura: None. Y. Yasunami: None.